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Biological membrane full topic summary

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Module
Biological membranes

Institution
OCR

Super in-depth summary of the entire biological membranes topic using all specification points answers are literal exam answers from most past papers which guarantees marks!

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Cell signalling = communication between cells where a molecule released by one cell causes a change in another cell Phospholipid bilayer → provides barrier for large or polar
Role of membranes within cells molecules
• Compartmentalisation→act as a barrier between
Glycoprotein Describe plasma membrane components
organelles and the cytoplasm Glycolipid Protein (extrinsic or intrinsic) • Phospholipid bilayer containing glycoproteins and glycolipids Channel or carrier proteins→ allow facilitated diffusion /active
• Site of chemical reactions→eg: mitochondrial membranes O • Hydrophobic fatty acid tails facing inwards transport
enzymes for respiration Phospholipid bilayer
• Hydrophilic phosphate head facing outwards
Glycoproteins/lipids → cell signalling, receptor sites, cell shape

...
• Form vesicles to transport substances in the cell • Transmembrane (intrinsic + extrinsic) proteins
• Provide enzyme attachment site Eit distr • Cholesterol between phospholipids

Role of membranes on cell surface in cell signalling What is the function of glycoproteins in cell membranes
• Signal molecule gets released by exocytosis Channel protein Cholesterol Phospholipid The role of cholesterol • Act as antigens in recognition of cells as self or non self
• Glycoproteins/ proteins/ glycolipids acts as receptors + have specific structures • Regulate fluidity • cell signalling
• Shape of receptors + signal are complementary • Stabilise membrane • Receptors for hormones or binding site
• Attachment of signal molecule causes change in cell so membrane allows entry for some through partially permeable • Manufacture vitamin D • Cell adhesion (hold cells in tissues)
membrane • Manufacture steroid hormones • Attach to H2O to stabilise membrane
Effects of temperature on membranes • Manufacture bile

Effect of solvent on membranes
High temperature Low temperature • Non polar solvents dissolve non polar solutes and the phospholipid bilayer is non polar
• So solvent [organic] disrupt and dissolve the cell membrane
• Phospholipids vibrate more + increase kinetic energy • Below O °C can cause increase permeability as proteins deform
• Increasing permeability to larger or charged molecules at low concentration or can destroy cells at high concentration
• Increasing gaps in the membrane • Ice crystals also pierce the cell membrane
• This is because hydrophobic tails are not repelled by the organic solvents
• The bilayer becomes more fluid Response from the membrane
• proteins denature
Cholesterol buffers the drop in temperature to prevent reduction in the membranes fluidity. It does this by preventing
Response from the membrane phospholipids from packing together too closely
At temperatures above °C → cholesterol pulls 45

phospholipids closer together by interacting with the
•
•
Saturated fatty acids become compressed
kinks in the tails push adjacent phospholipid
Biological membranes Outline diffusion of substances across the plasma membrane
phospholipid tails with the aim to reduce the increase in molecules away • Diffusion is the net movement of particles [molecules or ions] from an area of high to low
fluidity • some organisms like fish can change the concentration
composition of the fatty acids in the Why can glucose not pass through • Small non polar substances move through the membrane by diffusing through the bilayer
membrane via simple diffusion • Also lipid soluble molecules like steroid hormones can diffuse eg: C ,O , progesterone
• Glucose molecules are too large and non lipid
Outline facilitated diffusion of substances across the membrane soluble Passive transport = substances exchanged without input of metabolic energy from respiration and
• The net movement of particles down the concentration gradient across a partially permeable membrane • Phospholipid bilayer acts as a barrier to all
particles more using their own kinetic energy
via carrier or channel proteins water-soluble substances
• larger, polar or charged molecules can be facilitated by carrier or channel proteins eg: glucose, fructose, Active transport = movement of substances against the concentration gradient [low to high] using ATP
non lipid soluble, urea, ions and carrier proteins
• Highly specific / selective Examples: aquaporins, epithelial cells have chloride ion channels as well as synapses Examples of active transport. :
which have both chloride and calcium ion channels for transmission of electrical
Explain the process of endocytosis •• Waterfilled pores allowing diffusion +

impulse • H ions move out of companion cells in phloem tissue
'Gated' so part of protein opens + • Sodium ions out of cells in loop of henle
• plasma membrane invaginates when in contact closes depending on the molecule Explain the levels of potency in • Calcium ions into muscles for contraction
with the substance
• The membrane enfolds the molecule until fuses
• molecule binds to protein,so it undergoes terms of osmosis and the effects on • K ions into stomata to open them
+

to form a vesicle conformational change [of shape]
transport the molecule which then
to animal and plant cells • Ions move into root hair cells against concentration gradient
• The vesicle pinches Off and moves into detaches from the protein which reverts
cytoplasm to transfer material into the cell to its original shape • Isotonic solution
Animal cell → function properly Factors affecting diffusion rate
Osmosis = net movement of water from region of high water potential to Plant cell → remains placcid equal entering and removal of
Explain the process of exocytosis region of low water potential, down the water potential gradient, across a water • concentration gradient → steeper = faster diffusion
• Vesicles from Golgi fuse to plasma membrane
partially permeable membrane • Diffusion distance → greater distance/thicker membrane =
• Hypertonic solution slower diffusion
• Vesicle contents released outside the cell Water potential = The tendency of water molecules to diffuse in or out cell → H moves out, crenation, lost cytosol and cell death
Surface area →greater surface area= faster diffusion
↳ Animal

• ATP energy requires movement along of an area •
Plant cell → H moves out, plasmolysed, reduced cytoplasm volume and pulls
cytoskeleton to change cell shape, to engulf ↓ membrane from cell wall • Size of molecules → smaller= faster
materials, + fusion of membranes to fold Pure water Y = 8 Kpa Solutes [substances in a • Temperature → increased temperature = faster diffusion
vesicles • Hypotonic solution due to greater kinetic energy
solvent like water] = X Kpa
-

Animal cell → H moves into cell, (haemo)cytolysis, thin membrane
Plant cell → H 20 moves into the cell, turgid, cell wall withstands pressure and turgor pressure
resists entry of further water

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